1. Field of the Invention
The present invention relates generally to a printed circuit board having a weak magnetic field sensor and a method of manufacturing the same and, more particularly, to a printed circuit board having a weak magnetic field sensor, in which a soft magnetic core excitation circuit and a detection circuit are formed on the top and bottom of the printed circuit board to be perpendicular to each other, so that a weak magnetic field in a range similar to that of the geomagnetic field can be detected, and a method of manufacturing the same.
2. Description of the Related Art
Recently, weak magnetic field sensors are used in many applications, such as a navigation system depending on geomagnetism detection, a geomagnetism variation monitor for the prediction of earthquakes, some biomagnetism measurement, defect detection for metallic materials, magnetic encoding, a non-contact type potential meter, a current sensor, a torque sensor and a displacement sensor.
In particular, in order to provide a location information service for mobile phones and mobile terminals, sensors capable of accurately detecting current locations are required, and the weak magnetic field sensors for detecting the geomagnetic field and detecting current locations, shown in FIG. 1, are used as means for providing such location information.
FIG. 1 is a view showing the schematic construction of a conventional weak magnetic field sensor. FIG. 2a is a timing diagram of a magnetic field generated in a first magnetic core, and FIG. 2b is a timing diagram of a magnetic field generated in a second magnetic core. FIG. 2c is a timing diagram of a magnetic flux density generated in the first magnetic core, and FIG. 2d is a timing diagram of a magnetic flux density generated in the second magnetic core. FIG. 2e is a timing diagram showing a first induced voltage Vind1 and a second induced voltage Vind2 induced to a detection coil, and FIG. 2f is a timing diagram showing the sum of the first and second induced voltages Vind1+Vind2.
As shown in FIG. 1, the conventional weak magnetic field sensor includes first and second large rod-shaped magnetic cores 1a and 1b, excitation coils 2a and 2b wound around the first and second magnetic cores 1a and 1b, respectively, at regular intervals in regular directions so as to produce magnetic fields, and detection coils 3a and 3b wound to surround the first and second magnetic cores 1a and 1b at regular intervals in regular directions so as to detect the magnetic fields generated in the first and second magnetic cores.
The operation of the conventional weak magnetic field sensor is described with reference to FIGS. 2a to 2f. The internal magnetic field H1 of the first magnetic core 1a attributable to an Alternating Current (AC) excitation current is represented by ‘Hext (external magnetic field)+Hexc (magnetic field attributable to excitation coils),’ while the internal magnetic field H2 of the second magnetic core 1b is represented by ‘Hext−Hexc.’
Additionally, the magnetic flux density B1 of the first magnetic core 1a is represented by ‘Bext (magnetic flux density attributable to external magnetic field)+Bexc (magnetic flux densities attributable to excitation coils),’ while the magnetic flux density B2 of the second magnetic core 1b is represented by ‘Bext−Bexc.’
That is, the internal magnetic fields H1 and H2 and the magnetic flux densities B1 and B2 represented through the first and second magnetic cores 1a and 1b are generated in opposite directions.
In this case, the first and second induced voltages Vind1 and Vind2, which are generated by the first and second magnetic cores 1a and 1b and detected by the detection coils 3a and 3b, are represented as shown in FIG. 2e. 
In this case, since the detection coils 3a and 3b are wound to take the sum of flux changes generated in the first and second magnetic cores 1a and 1b, the voltage measured by the detection coils 3a and 3b is detected as shown in FIG. 2f because the first and second induced voltages Vind1 and Vind2 cancel out.
That is, the magnetic fields, which are attributable to the excitation coils 2a and 2b and are applied in the axial directions of the first and second magnetic cores 1a and 1b, are applied in opposite directions, so that the magnetic fields Hexc cancel out and are zero. However, the external magnetic fields Hext, which are applied in the axial directions of the first and second magnetic cores 1a and 1b, are applied in the same direction with respect to the first and second magnetic cores 1a and 1b, so that the external magnetic fields Hext do not cancel out.
Accordingly, the amount of the external magnetic fields Hext can be evaluated by measuring the amount of the sum of the first and second induced voltages Vind1 and Vind2.
However, the conventional weak magnetic field sensor has difficulty in maintaining location precision when the excitation coils 2a and 2b and the detection coils 3a and 3b are wound around the magnetic cores 1a and 1b, and further has a problem in that the precision of characteristic values is reduced because the conventional weak magnetic field sensor is easily affected by temperature, light and surface material.
Furthermore, since the excitation coils 2a and 2b and the detection coils 3a and 3b are wound directly around the magnetic cores 1a and 1b, the conventional weak magnetic field sensor is problematic in that the coils are frequently cut.
Furthermore, since the conventional weak magnetic field sensor has a large size and the power consumption thereof is high, the conventional weak magnetic field sensor is problematic in that it is not suitable for tendencies toward the miniaturization and lightweight of electronic products.
In order to overcome such problems of the conventional weak magnetic field sensor, U.S. Pat. Nos. 5,936,403 and 6,270,686 disclose weak magnetic field sensors, which are manufactured in such a way that an amorphous core is produced by laminating annularly etched amorphous plates on both sides of an epoxy substrate in which patterns are etched so that the top and bottom thereof are conducted to each other, and epoxy substrates on which X-coils and Y-coils are etched are laminated on the top and bottom of the amorphous core.
However, the inventions disclosed in U.S. Pat. Nos. 5,936,403 and 6,270,686 are problematic in that the amorphous core must be manufactured by laminating the annularly etched amorphous plates on the epoxy substrate with the patterns being aligned with the etched parts, and the epoxy substrates on which X-coils and Y-coils are etched must be laminated on the top and bottom of the amorphous core, so that a manufacturing process is complicated, the number of the layers of a circuit board are increasing and high costs are incurred.
Furthermore, the inventions disclosed in U.S. Pat. Nos. 5,936,403 and 6,270,686 are problematic in that the lands of coils are concentrated on the inside of the annular amorphous core, so that the turns of coils are limited. Accordingly, the density of the coils per unit length is low, so that the sensitivity of detection of a weak magnetic field is reduced and a tendency toward the miniaturization of electronic products is not accommodated.
In order to solve the above-described problems, Korean Pat. No. 432,662 filed on Mar. 9, 2002 by the present applicant discloses a weak magnetic field sensor using Printed Circuit Board (PCB) technology. This weak magnetic field sensor includes a first substrate on which first driving patterns and first pickup patterns are formed on both sides thereof, first layer bodies that are laminated on both sides of the first substrate and on which magnetic substances patterned in predetermined forms are formed, and second layer bodies that are laminated on the first layer bodies and in which second driving patterns and second pickup patterns are connected to the first driving patterns and the first pickup patterns, respectively. The magnetic substance, the driving patterns and the pickup patterns formed on the top of the first substrate, and the magnetic substance, the driving patterns and the pickup patterns formed on the bottom of the first substrate are perpendicular to each other.
However, the invention disclosed in Korea Pat. No. 432,662 has a problem in that it is difficult to provide a subminiature weak magnetic sensor to be mounted on a PCB according to demands for miniaturized, highly integrated and multi-functional electronic products.